This invention relates to dielectric fluids for electrical capacitors, particularly metallized polypropylene film capacitors.
In the manufacture of self-healing capacitors, the selection of the dielectric fluid has a substantial influence on the electrical characteristics of the capacitor. Self-healing occurs when dielectric breakdown of the metallized electrode occurs locally and the breakdown areas are healed. In other words, insulation of the capacitors is restored by flowing of the metal film portions around the short-circuited metallized films. Under powerful arcing dielectric fluid that has penetrated the film degrades and leads to an increase of the dissipation factor and leads to failure of the capacitors. Thus, in metallized polypropylene capacitors, the dielectric fluid should exhibit low swellability of the metallized polypropylene film, high viscosity and high contact angle with the film.